This application is based on Japanese Patent Applications No. 2001-341053 filed on Nov. 6, 2001 and No. 2002-218145 filed on Jul. 26, 2002 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection system with a fuel pressure sensor for detecting a pressure in an accumulator for pressurized fuel. Specifically, the present invention relates to a method and a system for learning and correcting an output characteristic of the fuel pressure sensor of the fuel injection system with the accumulator. The present invention may apply to a fuel injection system for injecting high pressure fuel accumulated in a common rail to an engine via an injector.
2. Related Art
Conventionally, a common rail fuel injection system is known as an accumulator fuel injection system. The system has a high pressure supply pump driven to rotate by a multi-cylinder diesel engine or the like. The pump is designed for pressurizing fuel and supply pressurized fuel to a common rail as an accumulator. The common rail accumulates high pressure fuel and distributes the high pressure fuel accumulated in the common rail to injectors. The injectors are mounted on respective cylinders of the multi-cylinder engine. The injectors inject the high pressure fuel accumulated in the common rail into respective combustion chambers of the cylinders.
According to the common rail fuel injection system, fuel pressure in the common rail is detected by a fuel pressure sensor. The fuel pressure in the common rail may be referred to as an actual common rail pressure. A supply amount of the high pressure supply pump is controlled by a feedback control such that the actual common rail pressure substantially coincides with a target common rail pressure. The target common rail pressure is set based on operating conditions of the multi-cylinder engine. Each of the fuel pressure sensors has an individual output characteristic. Therefore, each output of the fuel pressure sensors has a deviation from a reference output. Such the deviation can be suppressed in the manufacturing process of the fuel pressure sensor by narrowing a tolerance and managing severely. For example, in order to improve control accuracies of the common rail pressure, the accuracy of the single product of the fuel pressure sensor is severely adjusted within a narrowly set tolerance range.
However, according to the conventional common rail fuel injection system, there poses a problem that the tolerance of the fuel pressure sensor permitted during the manufacturing process constitutes the accuracy in controlling the system. Therefore, in order to improve the control accuracy, it is necessary to further improve the accuracy of the single product per se of the fuel pressure sensor. Such the improvement may increase the cost of manufacturing the fuel pressure sensor.
It is an object of the present invention to provide a fuel injection system that is capable of controlling a fuel injection system based on a fuel pressure in an accumulator accurately.
It is another object of the present invention to provide a fuel injection system that is capable of controlling a fuel pressure in an accumulator accurately.
It is a still another object of the present invention to provide a fuel injection system that is capable of reducing an influence of a deviation of a fuel pressure sensor on a fuel pressure control accuracy.
It is a yet another object of the present invention to provide a fuel injection system that is capable of significantly improving control accuracy of a system while considerably reducing cost of fabricating a fuel pressure sensor by learning and correcting a deviation in a characteristic of the fuel pressure sensor.
According to a first aspect of the present invention, a fuel injection system comprises a fuel pressure sensor and a controller operatively connected with the fuel pressure sensor. The fuel pressure sensor outputs an output signal indicative of a fuel pressure. The output signal and the fuel pressure defines an actual pattern of the output characteristic which may be varied from a basic pattern of the output characteristic. The controller controls at least one of components of the fuel injection system in response to the output signal of the fuel pressure sensor. The controller includes learning means and correcting means. The learning means detects the output signal corresponding to an atmospheric pressure which is outputted when the fuel pressure is expected to be lowered to an atmospheric pressure and learns the actual pattern of the output characteristic of the fuel pressure sensor based on the output signal corresponding to an atmospheric pressure. The correcting means corrects a control characteristic between the output signal and a control signal for the component based on the actual pattern of the output characteristic learned in the learning means. The control signal is determined in response to the output signal of the fuel pressure sensor so that the controller controls the component in an appropriate manner. As a result, it is possible to improve control accuracy even if the output characteristic of the fuel pressure sensor is varied in each sensor.
The output signal corresponding to the atmospheric pressure may be outputted while the engine is stopped. Further, The output signal corresponding to the atmospheric pressure may be outputted while the engine is stopped and a predetermined condition is satisfied. For example, the predetermined condition may be satisfied when the fuel pressure is lowered to an atmospheric pressure after stopping the engine. For example, the predetermined condition may be satisfied when a predetermined time period is elapsed after stopping the engine. For example, the predetermined condition may be satisfied when an amount of lowering an engine cooling water temperature or an intake temperature or a fuel temperature or an engine oil temperature after stopping the engine is equal to or larger than a predetermined value. The output signal corresponding to the atmospheric pressure may be outputted while the engine is stopped and in starting the engine after the predetermined condition has been satisfied. In addition, the correcting means may include output characteristic storing means and output characteristic changing means. The output characteristic storing means stores the output characteristic of the fuel pressure sensor. The controller is arranged to be responsive to the output characteristic stored in the output characteristic storing means. The output characteristic changing means changes the output characteristic based on the output characteristic learned in the learning means. The output characteristic storing means may initially store a basic pattern of the output characteristic, and the output characteristic changing means may change the output characteristic from the basic pattern to a learned pattern.
According to a second aspect of the present invention, by measuring a detected value of the fuel pressure sensor when the fuel pressure is lowered to an atmospheric pressure after stopping the engine, or when a predetermined time period is elapsed after stopping the engine, or when an amount of lowering an engine cooling water temperature or an intake temperature or a fuel temperature or an engine oil temperature after stopping the engine is equal to or larger than a predetermined value, inputting the measured detected value as a learning value in correspondence with the atmospheric pressure, and changing the basic pattern of the output characteristic of the fuel pressure sensor stored to the output characteristic storing means to a pattern after learning having an output characteristic using the learning value in correspondence with the atmospheric pressure inputted in stopping the engine. Therefore, it is not necessary to control accuracy of the fuel pressure sensor severely during the manufacturing and fabricating process. As a result, a considerable reduction in cost of fabricating the fuel pressure sensor can be achieved. Further, a deviation of the characteristic from a basic pattern of an output characteristic of a single product per se of the fuel pressure sensor can be learnt and corrected and therefore, control accuracy in the system can considerably be improved.
According to a third aspect of the present invention, by measuring a detected value of the fuel pressure sensor in starting the engine after the fuel pressure has been lowered to an atmospheric pressure after stopping the engine, or after a predetermined time period has elapsed after stopping the engine, or after an amount of lowering an engine cooling water temperature or an intake temperature or a fuel temperature or an engine oil temperature after stopping the engine has become equal to or larger than a predetermined value, inputting the measured detected value as a learning value in correspondence with the atmospheric pressure, and changing the basic pattern of an output characteristic of the fuel pressure sensor stored to the output characteristic storing means to a pattern after learning having an output characteristic using the learning value in correspondence with the atmospheric pressure inputted in starting the engine. Therefore, it is not necessary to control accuracy of the fuel pressure sensor severely during the manufacturing and fabricating process. As a result, a considerable reduction in cost of fabricating the fuel pressure sensor can be achieved. Further, a deviation of the characteristic from a basic pattern of an output characteristic of a single product per se of the fuel pressure sensor can be learnt and corrected and therefore, control accuracy in the system can considerably be improved.
In the present invention, the following exemplified arrangement may be advantageous in enhancing the advantages of the present invention. For example, a timing of starting the engine after the fuel pressure has been lowered to the atmospheric pressure after stopping the engine, or after the predetermined time period has elapsed after stopping the engine, or after the amount of lowering the engine cooling water temperature or the intake temperature or the fuel temperature or the engine oil temperature after stopping the engine becomes equal to or larger than the predetermined value, ay be indicated by a condition in which the ignition switch is made ON, electricity conduction to the starter is stopped and the learning permitting flag is made ON.
According to another exemplified arrangement of the present invention, the system converts the detected value of the fuel pressure sensor to the learning value in correspondence with the pattern after learning during operating the engine. The system inputs the learning value converted from the detected value. The system leans a deviation of the characteristic from the basic pattern of an output characteristic of a single product per se of the fuel pressure sensor, and corrects the output characteristic. The system reflects the detected value after learning and correcting to the control thereafter. For example, the system reflects the detected value corrected based on the learned amount to a common rail pressure control. Therefore, control accuracy in the system can considerably be improved. Additionally, it is possible to achieve a considerable reduction in cost of the fuel pressure sensor.
According to another exemplified arrangement of the present invention, the control performed after the learning and correcting procedure is a control for controlling a supply amount of the fuel supply pump by a feedback control such that an actual common rail pressure detected by the fuel pressure sensor substantially coincides with a target common rail pressure determined in accordance with an operating condition or an operating state of the engine. Thereby, the supply amount of the fuel supply pump, that is, the pressure of the fuel supplied from the fuel supply pump to the common rail, can accurately be proximate to a target common rail pressure determined in accordance with the operating condition or the operating state of the engine.
According to another exemplified arrangement of the present invention, the basic pattern of the output characteristic of the fuel pressure sensor is characterized in an output characteristic raised to the right before learning and correcting passing two points of an initial value in correspondence with the atmospheric pressure in stopping the engine and a high pressure side target value within a normally used range of the fuel pressure sensor. Further, as the high pressure side target value within the normally used range of the fuel pressure sensor, it is advantageous in forming the basic pattern to use a maximum value within the normally used range of the output characteristic of the fuel pressure sensor.
According to another exemplified arrangement of the present invention, the pattern after leaning of the output characteristic of the fuel pressure sensor is characterized in an output characteristic after leaning and correcting in which an inclination of the basic pattern of the output characteristic of the fuel pressure sensor is changed to pass two points of the learning value in correspondence with the atmospheric pressure inputted in stopping the engine and the high pressure side target value within the normally used range of the fuel pressure sensor. Further, as the high pressure side target value within the normally used range of the fuel pressure sensor, it is very advantageous in forming the pattern after learning to use a maximum value within the normally used range of the output characteristic of the fuel pressure sensor.
According to another exemplified arrangement of the present invention, the pattern after learning of the output characteristic of the fuel pressure sensor is characterized in an output characteristic after learning and correcting in which an inclination thereof is changed to pass two points of the learning value in correspondence with the atmospheric pressure inputted in stopping the engine and a value of an upper side of the high pressure side aimed value within the normally used range of the fuel pressure sensor.